Ester polyols are very useful for the production of polyurethane-based coatings and foams, as well as, polyester applications. The present invention provides a process using renewable resources, such as, oils and fats, fatty acids, and fatty acid alkyl esters derived from plants and animals to produce polyurethane foams and lubricants. Some chemicals derived from vegetable oils and animal fats are oleochemicals, which can have structures similar to petrochemicals, which are chemicals derived from petroleum. As the price of crude oil increases, an increase in demand from oleochemicals is expected.
Plant oils and animal fats are primarily composed of triglycerides that can be readily hydrolyzed to their component fatty acids and glycerin. Fatty acids obtained from either source are typically composed of mixtures of saturated and unsaturated fatty acids and fatty acids obtained from plant oils are usually richer in unsaturated fatty acids. Saturated fatty acids typically have higher melting points and much lower solubilities in a variety of solvents and other components than unsaturated fatty acids and partial removal of saturated fatty acids is practiced in certain applications. As described in U.S. Pat. No. 2,813,113 and related patents, fatty acids may be subjected to oxidative ozonolysis which involves an initial reaction with ozone to form intermediate ozonides followed by the oxidation of such intermediates with oxygen and a catalyst. This process generates mixtures of monoacids and diacids which are commonly called ozone acids. The oxidative ozonolysis process cleaves all double bonds in unsaturated fatty acids and introduces carboxylic acid functionality at all original double-bonded carbon atoms present in unsaturated fatty acids. Based on U.S. Pat. No. 2,813,113, the ozonolysis stage must be performed at relatively low temperatures and the viscosity of the intermediate ozonides is advantageously kept below minimum values at low temperatures. Typically a solvent is used in the oxidative ozonolysis process to help reduce reaction mixture viscosities. Since the viscosities of unsaturated fatty acids can be less than the viscosity of the corresponding saturated fatty acid, partial removal of saturated fatty acids can result in further reduction of reaction viscosity. Also, partial removal of saturated fatty acids, which do not undergo reaction with ozone or oxygen, before oxidative ozonolysis can increase the efficiency of mixing and reaction of unsaturated fatty acids with gaseous ozone and oxygen during the two-stage oxidative ozonolysis process. Removal of non-reactive saturated fatty acids prior to oxidative ozonolysis also can reduce the reactor size required to produce a certain amount of cleaved product. Thus, there is a rationale for partial removal of saturated fatty acids from unsaturated fatty acid feedstocks before undergoing oxidative ozonolysis.
A common industrial method to purify fatty acids involves fractional crystallization of saturated fatty acids from unsaturated fatty acids at relatively low temperatures either without or with the aid of solvents. This approach is based on the fact that saturated fatty acids typically have higher melting points and lower solubilities in other components than unsaturated fatty acids. When solvents are not used, mixtures of fatty acids are first heated so that the sample is fully liquid and these samples are then slowly cooled to temperatures of about 35° F. which results in partial crystallization of saturated fatty acids while the unsaturated fatty acids mainly remain in the liquid state. The solidified saturated fatty acids are then typically removed by filtration involving application of pressure to squeeze the liquid from the solid mass. Disadvantages of this approach are that the lower temperature must be reached slowly to obtain effective selective fractionation and this process results in only partial fractionation of saturated fatty acids from unsaturated fatty acids. Fractional crystallization has also been performed by initially dissolving fatty acid mixtures in solvents such as methanol or acetone and decreasing the temperature to −15° C. when methanol is used and −50° C. when acetone is used. A disadvantage of this approach is that these flammable solvents must be recovered and recycled to enhance the economics of this process. Tallow, a common source of fatty acids, consists of about 47 percent of the mono-unsaturated fatty acid oleic acid. When solvent-based crystallization techniques are applied to tallow, the product recovered from solvent contains 70-80 percent oleic acid.
The conventional method of fractionation of fatty acids by crystallization is shown in FIG. 1. FIG. 1 also shows the oxidative ozonolysis of the fractionated fatty acids to form a mixture of ozone acids that are then converted to product ester polyols. Another reason to remove saturated fatty acids from mixtures of saturated and unsaturated fatty acids is the enhanced performance of ester polyols containing reduced quantities of saturated fatty acids.